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Optimization Strategies for Midline and Peripheral Tumours for IMRT and RapidArc - A Phantom Study


S.A Syam Kumar

s kumar*, A Silpa, B Resmi, C Suja, Malabar Cancer Centre, Kannur, Kerala

MO-B-Salon EF-12 Monday 10:00:00 AM - 12:00:00 PM Room: Salon EF

Purpose:
To evaluate the optimization strategies for midline and peripheral tumours for IMRT and RapidArc treatments.

Methods:
Homogeneous phantom was CT scanned and PTV was delineated for two different positions (midline and periphery). Two organs at risk with different shapes (organ at risk 1, organ at risk 2) were created. Different plannings were done with organ at risk 1, placed at distance of 0.5cm and 2cm. Also organ at risk 2, placed at a distance of 1cm and 2.5cm from the border of PTV along the central axis.Planning has been done for IMRT using 9 fields and RapidArc with double arc. Beam has been equally placed for IMRT plans and RapidArc plans utilize full 360 degree gantry rotation.

Results:
Dose homogeneity was almost similar for tumours in the midline where organs at risk are far. But RapidArc plans show superior dose homogeneity in PTV, when the target is situated at the periphery and organs at risk are very near (HI-2.67 for Rapid Arc and HI 4.03 for IMRT). Target coverage was better for all RapidArc plans with maximum CI 1.01. The sparing of organ at risk in terms of the maximum dose was better in RapidArc. A considerable reduction in organ at risk mean dose (12.37% for organ at risk 1 and 10.23% for organ at risk 2) was observed with RapidArc technique for peripheral tumors. For healthy tissue, no significant changes were observed in terms of the mean dose and integral dose.But RapidArc plans show a reduction in the volume of the healthy tissue irradiation above V10Gy for targets at the periphery and OAR near.

Conclusion:
Either IMRT or RapidArc can be chosen for tumours in the midline. Particularly RapidArc treatment can be recommended for tumours which are situated at the periphery.



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